Splice Isoforms of the Polyglutamine Disease Protein Ataxin-3 Exhibit Similar Enzymatic yet Different Aggregation Properties

Abstract

Protein context clearly influences neurotoxicity in polyglutamine diseases, but the contribution of alternative splicing to this phenomenon has rarely been investigated. Ataxin-3, a deubiquitinating enzyme and the disease protein in SCA3, is alternatively spliced to encode either a C-terminal hydrophobic stretch or a third ubiquitin interacting motif (termed 2UIM and 3UIM isoforms, respectively). In light of emerging insights into ataxin-3 function, we examined the significance of this splice variation. We confirmed neural expression of several minor 5′ variants and both of the known 3′ ataxin-3 splice variants. Regardless of polyglutamine expansion, 3UIM ataxin-3 is the predominant isoform in brain. Although 2UIM and 3UIM ataxin-3 display similar in vitro deubiquitinating activity, 2UIM ataxin-3 is more prone to aggregate and more rapidly degraded by the proteasome. Our data demonstrate how alternative splicing of sequences distinct from the trinucleotide repeat can alter properties of the encoded polyglutamine disease protein and thereby perhaps contribute to selective neurotoxicity.

Chronic Treatment with 17-DMAG Improves Balance and Coordination in A New Mouse Model of Machado-Joseph Disease

“…In this work, we have generated a new transgenic mouse model expressing at near the same cDNA variant of ataxin-3 as in our previous CMVMJD94 model, ATXN3c-which corresponds to the most predominant variant of the protein in the brain [38], but with an increased number of glutamine residues (135Q). Moreover, we tested a potent Hsp90 inhibitor, 17-DMAG, that was able to improve the motor phenotype and the neuropathological features of CMVMJD135 mice.…”

SUMOylation of the brain-predominant Ataxin-3 isoform modulates its interaction with p97

“…Interestingly, SUMO conjugation did not modify the interac- behavior [14,15,30,39,53,54], it is hypothesized that self-assembly of 524 polyQ-expanded Atx3 can result from an imbalance in the association 525 with the native molecular partners, whose interactions might be further 526 modulated by posttranslational modifications [17,18]. Here it is shown 527 that both non-pathogenic and expanded Atx3 are SUMOylated at 528 K356 and that only the 3UIM Atx3 splice isoform, which is predominant 529 in the brain [40], but not the 2UIM Atx3 isoform, is SUMOylated, sug-530 gesting that this posttranslational modification might have a role in 531 the control of Atx3 neuronal functions, therefore impacting MJD.…”

Deubiquitylases From Genes to Organism

“…This progressive condition is characterized by polyQ expansion in the ataxin 3 (ATXN3) gene (168). The NH 2 -terminal Josephin domain possesses deubiquitylating activity (30, 227), while the COOH terminus of the most abundant isoform contains two UIM domains followed by the polyQ sequence and then a third UIM (89). The etiology of MJD is linked to the formation of cellular aggregates once a threshold of polyQ extension has been reached, in common with other polyQ diseases such as Huntington's.…”